How does runif work with array?

I try to understand a small simulation code. However, I just confused about the result from runif function stored in an array.

Here is the code:

 N=10
 dim=3
 v = array(NA, c(dim, dim))
 x <- array(NA, dim=c(N, dim))
  for(s in 1:N)
     {
  w <- runif(dim)
  x[s,1] <- w[1]
  v[1,1] <- w[1]
  }
 x

w will be 3 uniform numbers. x[s,1] is the first column of x array. x[s,1] <- w[1] that means all the values in the first column must take the first value of the vector w. However, when I print x I got 10 different values. It is really confused me. When I try to use x[1,1] <- w[1], it works just fine! However, x[s,1] <-w[1] is just x[,1] <- runif(N) see the comments of @zx8754.

Do I miss something? How does this code work? Any help, please?